South Africa Wine Technical Yearbook 2025

MARCH

Winery wastewater irrigation (Part 2): Soil chemical responses on poorly drained soils By Reckson Mulidzi & Carolyn Howell

physicochemical soil properties. The application of WWW with high levels of K + and Mg 2+ reduced soil structural stability and hydraulic conductivity. 7 The current trend of replacing sodium hydroxide with K + -based cleaning detergents in wineries could lead to increased K + levels in WWW. 7 Accumulation of high levels of K + in the soil is regarded as a potential problem by regulators and wine industry, because of the effect on soil structure and the accumulation of salts. 8 Disposal of WWW through land application has the potential to increase levels of soluble K + and the potassium exchange percentage (EPP) in soils as most K + in wastewater is available immediately. 9 It was previously shown that soils with low clay content retained less K + in the exchangeable form, while soils with higher clay content retained K + to a much greater extent. 10 The application of WWW with K + and Na + levels of approximately 400 mg/L to pastures and woodlots over the long term resulted in the accumulation of soil K + levels of 1 400 mg/kg. 11 High levels of Na + in the soil cause soil dispersion. Dispersion actually occurs when high-Na soils are irrigated with fresh relatively low-salinity water. It was previously believed that problems occur only when the exchangeable sodium percentage (ESP) of the soil is above 15. However, research in various countries such as Australia and South Africa has shown that in some soils Na + causes problems

Abstract The use and availability of wastewater for irrigation have increased globally and the disposal of wastewater is governed by stringent legislations. Most wineries in South Africa dispose their wastewater through land application. The land application of winery wastewater (WWW) results in accumulation of soil potassium (K + ) and sodium (Na + ). This can reduce soil structural stability and hydraulic conductivity. Therefore, the objective of the study was to investigate the effect of WWW irrigation on soil chemical properties and potential environmental impacts at a new paddock at a winery near Stellenbosch where no WWW had previously been applied. Due to the high volumes of WWW irrigation plus rainfall, the inevitable over-irrigation leached large amounts of cations, particular K+ and Na+, beyond the 90 cm depth. Unfortunately, the leached elements are bound to end up in natural water resources in the long run. Irrigation with WWW did not have a pronounced effect on soil pH (KCl) . The study confirmed that injudicious irrigation with untreated WWW poses a serious environmental hazard, particularly where crops in sandy soils are irrigated. Land disposal can only be recommended where the wastewater application does not exceed the water requirement of the grazing crop, or any other agricultural crop. This means that the WWW needs to be distributed on an area of land that is big enough so that the daily applications does not cause over-irrigation. Soil chemical status should be determined at least annually.

Introduction The use and availability of wastewater for irrigation have increased globally and the disposal of wastewater is governed by stringent legislations. 1 Most wineries in South Africa dispose their wastewater through land application. 2 This is done by irrigating small areas of cultivated pasture with the winery wastewater (WWW) or ponding, with the former more general. 3 The land application of WWW results in accumulation of soil potassium (K + ) and sodium (Na + ). There is also leaching of calcium

(Ca 2+ ) and magnesium (Mg 2+ ), which leads to the long-term instability of soil structure. 2,4 This will affect the soil’s hydraulic conductivity. Long-term application of WWW on pastures resulted in the accumulation of soil K + that has the potential to leach into groundwater and other water sources. 5 Although the effects of using wastewaters with high K + concentrations for irrigation have not been researched extensively, irrigating with such K-rich wastewaters could be advantageous to overall soil fertility. 6 However, the long-term application thereof could result in the alteration of

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TECHNICAL YEARBOOK 2025